Fluid containment system

ABSTRACT

A fluid container comprises spaced horizontal and vertical elongated support members, intermediate wall, outer membrane, inner wall and inner membrane.

O Unlted States Patent 1 [111 3,730,375 Reed et al. 1 May 1, 1973 [54] FLUID CONTAINMENT SYSTEM 3,547.302 12/1970 Jackson ..l 14/74 A 3,477,606 11/1969 Schwendtner ..220/ l5 [75] Inventors: Edwln E. Reed; E. Kleinmann, both of Bartlesville, Okla.

[73] Assignee: Phillips Petroleum Company, Bart- Primary Examiner-Samuel B. Rothberg lesville, Okla. Assistant Examiner-Allan N. Shoop [22] Filed: Dec. 27, 1971 Attorney-Qungg and Oberlm [21] Appl. No.: 212,119

[57] ABSTRACT [52] US. Cl. ..220/9 LG, 220/10, 220/15 A fluid container comprises spaced horizontal and [51] "365d 25/18 B65d 7/22 365d 25/00 vertical elongated support members, intermediate [58] Fidd 0f Search A, 9 LG, 9 D, n outer membrane, inner l and inner 220/15; 114/74 A brane' [56] References Cited 8 Claims, 5 Drawing Figures UNITED STATES PATENTS 3,339,778 9/1967 Herrenschmidt .220/9 LG PATENTH] MY 1 I975 saw 1 BF 2 7 MFW 37 F Q a INVENTORS F/G. E.E. REED E. E. KLEINMANN ATTORNEYS FLUID CONTAINMENT SYSTEM BACKGROUND OF INVENTION This invention relates to fluid containment systems. In one aspect it relates to fluid containment systems especially adapted for containing cold liquids in liquid transport ships.

In providing storage tanks for use in the maritime transport of liquefied natural gas (LNG) three of the important considerations are l. safe fluid tight storage space,

2. adequate thermal insulation to minimize boiling of the stored product and to protect the ships structure from exposure to extreme cold,

3. cost of construction.

In various degrees the first two of these considerations have been satisfied by systems previously proposed for use in existing LNG tankers. However, these systems have been expensive to construct.

An object of the present invention is to provide safe, fluid tight storage space, with adequate thermal insulation, at reasonable cost.

SUMMARY OF INVENTION According to our invention a fluid holding tank comprises inner and outer fluid tight membranes, each membrane backed by a substantially continuous rigid wall, the membranes and walls being supported by a structure of horizontal and vertical members retained in position by a wall of supporting structure. The supported structure in one preferred embodiment is the inner hull of a ship. Further according to our invention the vertical support members are attached to the wall of the supporting structure, the horizontal members are supported by and attached to the vertical members on the inside thereof, an intermediate wall is provided of a plurality of rigid wall members, an outer fluid tight membrane rests against the intermediate wall, an inner wall also composed of a plurality of rigid wall members is situated on the inside of the outer membrane and in turn an inner membrane rests against the inner wall.

Referring to the drawing,

FIG. 1 is an elevation of a portion of the supporting structure of a liquid holding tank according to our invention.

FIG. 2 is a vertical cross section taken along the line 2-2 of FIG. 1.

FIG. 3 is a vertical cross section through the tank.

FIG. 4 is a vertical cross section of an embodiment of the invention in which passageways are provided for free vapor circulation.

FIG. 5 is a horizontal cross section of an embodiment in which the rigid wall members are supported by pins through the complementary fasteners supporting the membranes.

In the structure illustrated in FIGS. 1, 2 and 3, a plurality of outer elongated support members 11 in the form of wooden stringers are resting against the metal inner hull 12 of a double hull tanker and are attached thereto by means of a plurality of bolts 13 welded to inner hull l2. Bolts 13 extend through holes drilled through outer support members 11 which are held in place by nuts 14. A plurality of outer support members 11 in generally parallel relation with each other are positioned around the periphery of the space encom passed by the tank. A plurality of inner elongated support members 15 are supported in contact with the outer support members 1 1 and are attached thereto by a plurality of bolts. Bolts 16 have their heads in recesses 17 of support members 11 whereby, when the nuts 18 are tightened pulling support members 15 into close contact with support members 11, the heads of the bolts 16 are pulled into the recesses out of contact with inner hull 12. Thus it will be seen that no direct metal heat path exists between inner hull l2 and inner support members 15. As illustrated, members 15 are made of wood.

Outer J-strap fasteners 21 are attached to inner support members 15 by suitable fastening means 22, for example, nails. Outer rigid wall members 23 made of plywood sheets are supported on said inner support members forming an intermediate wall, spaced from said outer support members. One suitable means of attachment is by means of adhesive (not shown).

An outer fluid tight membrane 26 made of a plurality of sheets 27 of thin Invar metal, is attached to said inner support members 15 by means of a plurality of S- strap fasteners 28 which link with outer J-strap fasteners 21, S-strap fasteners 28 being welded between mating edges of sheets 27 as illustrated. These S-strap fasteners are complementary fasteners cooperating with the outer J -strap fasteners.

Inner rigid wall members 31 made of plywood sheets form an inner wall supported by outer membrane 26, for example by means of an adhesive (not shown). Inner fluid tight membrane 33, formed by sheets 34 of thin Invar metal, are held in place by inner .l-strap fasteners 36 welded between mating edges of sheets 34 and linked with the outer portion of S-strap fasteners 28.

A plurality of blocks or batts of insulation 37 are positioned adjacent inner hull 12 between outer support members 11 and between inner support members 15 covering outer support members 1 1.

In one suitable construction, outer support members 11 and inner support members 15 are both made of nominal 2 X 6 wooden members and the sheets 27 and 34 are made of Invar metal having a thickness of about 0.020 inch.

The entire structure can withstand considerable movement due to racking of the ships hull. For example, the angle between outer support members 11 and inner support members 15 can change as the hull is twisted, individual wall members 23 or 31 can move with respect to each other, membranes 26 and 33 can move with respect to each other and with respect to support members 11 and 15, etc.

As illustrated in FIG. 4, inner rigid wall members 49 embody means to facilitate vapor flow through and around these members. Such means take the form of perforations 43, chamfers 44 and grooves 46. Such perforations, chamfers and grooves make it easier for gas and vapor to circulate throughout the space between outer membrane 47 and inner membrane 48. This is desirable to permit effective inert gas purge of this space and to detect any leakage 'of product into this space. Such purge and detection can be accomplished by circulating an inert gas into the space in question and analyzing the return purge gas for evidence of the stored product or leakage can be detected by merely checking for flow from this space without circulating purge gas between membranes 47 and 48. Throughout the operation the pressure in this space should be maintained at or near atmospheric pressure and, in any event, not greater than the pressure inside inner membrane 48.

If desired, the perforations, chamfers and grooves also can be provided in outer wall members 54. It is also desirable to permit gas purge of the space outside outer membrane 47 to detect leakage of product into this space. Such purge and detection can be accom plished in the same manner as for the space between the membranes.

It will be understood of course that various forms and combinations of perforations, chamfers and grooves can be utilized to obtain the desired results. For example, the wall members can be chamfered on some or all of their edges, grooves can be placed in the wall members in various configurations, for example parallel strips of in crossing strips, etc. Perforations can be provided in various patterns by drilling and/or punching holes through the members.

FIG. 5 illustrates means by which the rigid wall members can be supported by the fastening members used to support the membranes. As shown in FIG. 5, inner wall members 49 are supported by the inner portion of C-strap fasteners 50. Depressions 51 and 52 are placed in the ends of the rigid wall members and a pin 53 extends through the C-fastener 50. Of course a plurality of such support pins can be used and the pins can be welded into the fastener if desired.

Such support means as illustrated in FIG. 5 is particularly adapted for supporting the inner rigid wall members 49 of FIG. 4 or 31 of FIG. 3. However, such means can also be used for outer rigid wall members 54 or 23 if desired.

Of course, reasonable variation and modification are possible within the scope of the invention. For example, various type of fastening means can be used for attaching outer J-straps 21 such as nails, staples, screws, or J-straps 21 can be attached by a suitable adhesive. In most instances it is preferred and in some instances it is necessary that wall members 23 extend over fasteners 22 to provide additional holding means which is needed when the pressure outside inner membrane 48 is greater than the pressure within the storage space. As indicated above, in normal operation the pressure between the two membranes should be less than the pressure within the storage space. However, this pressure differential may be reversed if a leak occurs in inner membrane 48 or due to an increase in pressure between the membranes inadvertently or for the purpose of testing the inner membrane. The reversed pressure differential can also occur during cargo discharging by pumping at a rate sufficient to reduce the pressure in the storage space to a value below that existing between the membranes. Of course, instrumentation is provided to avoid either buildup of pressure between the membranes or reducing the pressure within the tanks to an undesirable low value and therefore these two situations require an instrumentation malfunction. The fastening means illustrated in FIG. 4 provides additional holding power since the fastener is in shear upon a reverse pressure differential.

S-strap fastener 28 and C-strap fastener 50 can be made by welding in place two J-strap fasteners. Alternatively, although in most instances less desirable, the complementary fastener can be a .I-strap fastener linking with outer J-strap fastener 21 of FIG. 3 or the outer J-strap fastener of FIG. 4 and welded to both the inner and outer membranes.

Various kinds of wood can be utilized for the various wooden structural members. Structural members also can be made of a single solid piece of wood or can be built up, i.e., laminated. For example, the members 42 of FIG. 4 can be a single grooved member or can be laminated as illustrated. Plywood having a honeycombed inner structure can be utilized for the rigid wall members.

Various types of insulation are suitable for the batts or blocks 37. Preferably these blocks fit together very closely to avoid both undesirable working of the edges against each other due to racking of the ship and to minimize heat transfer between the blocks. However, if desired, the insulation can be vapor permeable. This assists in providing for free vapor flow in the space outside the outer membrane and, depending upon the exact structure selected, will minimize or eliminate entirely the necessity for providing vapor passageways in the outer rigid wall members.

Other modifications and variations will occur to one skilled in the art utilizing the invention disclosed herein.

That which is claimed is:

1. In combination with an outer load carrying structure, a fluid holding tank comprising:

a plurality of outer elongated support members made of a low heat conductivity material spaced apart in parallel relation resting against and attached to a supporting wall of said load carrying structure;

a plurality of inner elongated support members spaced apart in parallel relation supported in contact with said outer support members and spaced from said supporting wall;

a plurality of outer rigid wall members forming an intermediate wall supported on said inner support members, spaced from said outer support members;

an outer fluid tight membrane attached to said inner support members and extending over the inner surface of said intermediate wall;

a plurality of inner rigid wall members forming an inner wall supported by said outer membrane; and

an inner fluid tight membrane attached to said outer membrane and to said inner support members and extending over the inner surface of said inner wall.

2. The combination of claim 1, wherein said inner support members are attached to said outer support members by a plurality of metal attaching means which do not contact said supporting wall.

3. The combination of claim 1, wherein said outer membrane is attached to said inner support members through a plurality of outer J-strap fasteners fastened on said inner support members and a plurality of complementary fasteners fastened to said outer membrane and linked with said outer .I-strap fasteners.

4. The combination of claim 3 wherein said complementary fasteners are S-strap fasteners comprising outer bends linked with said outer .I- strap and inner bends; and

said inner membrane is attached to said inner support members through a plurality of inner .I-strap fasteners fastened to said inner membrane and linked with said inner bends of said S-strap fasteners. 5. The combination of claim 1 wherein said outer support members, said inner support members, said outer rigid wall members and said inner rigid wall members are made of wood; and

said outer membrane and said inner membrane are made of Invar metal.

6. The combination of claim 5 wherein said outer membrane and said inner membrane are fabricated from a plurality of sheets of lnvar metal welded together.

7. The combination of claim 3 wherein said outer membrane and said inner membrane are fabricated from a plurality of metal sheets welded together; and

said complementary fasteners are welded between mating edges of said metal sheets of said outer membrane.

8. The combination of claim 4 wherein said outer membrane and said inner membrane are fabricated from a plurality of metal sheets welded together;

said S-strap fasteners are welded between mating edges of said metal sheets of said outer membrane; and

said inner J-strap fasteners are welded between mating edges of said metal sheets of said inner membrane. 

1. In combination with an outer load carrying structure, a fluid holding tank comprising: a plurality of outer elongated support members made of a low heat conductivity material spaced apart in parallel relation resting against and attached to a supporting wall of said load carrying structure; a plurality of inner elongated support members spaced apart in parallel relation supported in contact with said outer support members and spaced from said supporting wall; a plurality of outer rigid wall members forming an intermediate wall supported on said inner support members, spaced from said outer support members; an outer fluid tight membrane attached to said inner support members and extending over the inner surface of said intermediate wall; a plurality of inner rigid wall members forming an inner wall supported by said outer membrane; and an inner fluid tight membrane attached to said outer membrane and to said inner support members and extending over the inner surface of said inner wall.
 2. The combination of claim 1, wherein said inner support members are attached to said outer support members by a plurality of metal attaching means which do not contact said supporting wall.
 3. The combination of claim 1, wherein said outer membrane is attached to said inner support members through a plurality of outer J-strap fasteners fastened on said inner support members and a plurality of complementary fasteners fastened to said outer membrane and linked with said outer J-strap fasteners.
 4. The combination of claim 3 wherein said complementary fasteners are S-strap fasteners comprising outer bends linked with said outer J-strap and inner bends; and said inner membrane is attached to said inner support members through a plurality of inner J-strap fasteners fastened to said inner membrane and linked with said inner bends of said S-strap fasteners.
 5. The combination of claim 1 wherein said outer support members, said inner support members, said outer rigid wall members and said inner rigid wall members are made of wood; and said outer membrane and said inner membrane are made of Invar metal.
 6. The combination of claim 5 wherein said outer membrane and said inner membrane are fabricated from a plurality of sheets of Invar metal welded together.
 7. The combination of claim 3 wherein said outer membrane and said inner membrane are fabricated from a plurality of metal sheets welded together; and said complementary fasteners are welded between mating edges of said metal sheets of said outer membrane.
 8. The combination of claim 4 wherein said outer membrane and said inner membrane are fabricated from a plurality of metal sheets welded together; said S-strap fasteners are welded between mating edges of said metal sheets of said outer membrane; and said inner J-strap fasteners are welded between mating edges of said metal sheets of said inner membrane. 